Thanks! `readandwrite` looks exactly like what I need. I'll try it out. I don't mind too much that this (and related) commands return a tuple, although I'd prefer the alternative discussed in issue 9659. What I'd much prefer is for them to be documented under "Running external programs", and not under "Essentials", where I never thought to look for them. Once I get a better handle for how they work, I'll try to improve the docs in this respect.
-- mb On Wed, Jun 17, 2015 at 1:05 PM, Kevin Squire <[email protected]> wrote: > `open(cmd, "w")` gives back a tuple. Try using > > f, p = open(`gnuplot`,"w") > write(f, "plot sin(x)") > > There was a bit of discussion when this change was made (I couldn't find > it with a quick search), about this returning a tuple--it's a little > unintuitive, and could be `fixed` in a few different ways (easiest: > returning a complex type that can be written to and read from), but it's > probably been off most people's radar. If you're up for it, why don't you > open an issue (if one doesn't exist). > > Anyway, for your particular application, you probably want `readandwrite`: > > help?> readandwrite > search: readandwrite > > Base.readandwrite(command) > > Starts running a command asynchronously, and returns a tuple > (stdout,stdin,process) of the output stream and input stream of the > process, and the process object itself. > > Which *also* returns a tuple (but at least now you know). > > See also http://blog.leahhanson.us/running-shell-commands-from-julia.html, > which has a full rundown of reading and writing from processes. > > Cheers! > Kevin > > On Wed, Jun 17, 2015 at 9:03 AM, Miguel Bazdresch <[email protected]> > wrote: > >> Hello, >> >> Gaston.jl is a plotting package based on gnuplot. Gnuplot is command-line >> tool, so I send commands to it via a pipe. I open the pipe (on Linux) with >> a ccall to "popen", and write gnuplot commands to the pipe using a ccall to >> fputs. >> >> This works fine, but I'm trying to see if Julia's native pipe and stream >> functionality can make this process more Julian and, in the process, more >> cross-platform. The documentation is encouraging: >> >> "You can use [a Cmd] object to connect the command to others via pipes, >> run it, and read or write to it." and "Julia provides a rich interface to >> deal with streaming I/O objects such as terminals, pipes and TCP sockets." >> Unfortunately, I just can't figure out how to use Julia's functionality for >> this purpose. This is what I've tried (I am on Julia 0.3.9): >> >> First, I tried using `open` with read and write: >> >> julia> f=open(`gnuplot`,"r+") >> ERROR: ArgumentError("mode must be \"r\" or \"w\", not \"r+\"") >> >> So I tried with write only: >> >> julia> f=open(`gnuplot`,"w") >> (Pipe(open, 0 bytes waiting),Process(`gnuplot`, ProcessRunning)) >> >> So far, this looks good. I can see a gnuplot process running. >> >> Then I try to `write` to the pipe: >> >> julia> write(f,"plot sin(x)") >> ERROR: `write` has no method matching write(::(Pipe,Process), >> ::ASCIIString) >> >> OK, so let's try with `println`: >> >> julia> println(f,"plot sin(x)") >> (Pipe(open, 0 bytes waiting),Process(`gnuplot`, ProcessRunning))plot >> sin(x) >> >> and no plot is produced. >> >> I can't figure out how to read from the pipe, either: >> >> julia> readbytes(f) >> ERROR: `readbytes` has no method matching readbytes(::(Pipe,Process)) >> >> julia> readall(f) >> ERROR: `readall` has no method matching readall(::(Pipe,Process)) >> >> I'd appreciate any pointers. Thanks! >> >> -- mb >> >> >
